Phase Change Memory (PCM) is a non-volatile memory commonly used in re-writable data storage media such as CDs and DVDs. The phenomenon relies on the property of chalcogenide materials to exhibit unlimited and reversible phase change between their amorphous and crystalline phase, each of theses phases having distinct optical and electrical properties. In electronic devices, each of these phases is associated to one bite (0 or 1), which enables data storage. The chalcogenide materials may have different compositions. The chalcogenide materials are frequently alloys made of tellurium, germanium, antimony, and/or selenium. Ge2Sb2Te5 (GST) is one of the most studied chalcogenide materials. However, although the deposition of GST films using CVD or ALD technique has been reported, the search remains for adequate precursors and deposition processes suitable for the commercial deposition of GST.
GST films were obtained by Ritala and his team at 90° C. in thermal ALD mode using germanium, antimony, and tellurium precursors which exhibit a very high reactivity between each others (Ritala et al., Microelectronic Engineering 86 (2009) 1946-1949). GeCl2-dioxane, Te(SiEt3)2 or Te(SitBuMe2)2 were used. The reaction that enables the deposition at low temperature was already hinted by Razuvaev (Razuvaev et al., Organosilicon and organogermanium derivatives with silicon-metal and germanium-metal bonds, 1969, Vol. 19, Issue 3, p. 353-374), and is as follows:Te(SiR3)2(g)+MCl2(g)→MTe(s)+2R3SiCl(g)In these articles, the poor quality of the films, as well as the use of a plasma power, which can damage the sub-layer and may not allow enough uniform coverage of patterned wafers, was a problem. The use of GeCl2-dioxane may also be a problem as this molecule exhibits a high melting point (178-180° C.) and a low volatility, making it a less than ideal candidate for CVD/ALD deposition techniques.
WO2009/132207 to ASM International N.V. disclosed atomic layer deposition processes for forming Te-containing films, including Ge—Te and Ge2Sb2Te5 (GST). The Ge-containing precursors used in the disclosed processes include GeX2 with X being F, Cl, Br, or I and adducted derivatives of GeX2, such as GeCl2-dioxane. Exemplary depositions using GeBr2 and GeCl2-dioxane precursors are provided.
In most of the work published up to now, the poor quality of the films, as well as the use of a plasma power, which can damage the sub-layer and may not allow sufficiently uniform coverage of patterned wafers, is a problem. The use of GeCl2-dioxane may also be a problem as this molecule exhibits a high melting point (178-180° C.), which raise handling as well as delivery issues, and volatility mismatch with the tellurium and antimony molecules.
Accordingly, there exists a need for materials which allow deposition of germanium-containing films through CVD and ALD techniques.